We use Cisco ACI for data center software-defined networking. Instead of restricting ourselves to older Cisco data center networking like 6500 switches for servers or Nexus devices or 6500 core switches, I personally like the flexibility of Cisco ACI to grow the data center footprint and stability Cisco was promising with new 6500 like architecture. That is when I decided to go for software-defined networking, where you can program things and do it better.
We also had something coming up on the horizon where two different MUFG entities were likely to come together and start consolidating Infrastructure, namely MUFG Bank and MUFG Securities. Cisco ACI is like cloud data center networking or cloud networking in your private DCs, where you have a multi-tenancy. The real use case for Cisco ACI was to segment two different entities and put them on the same network hardware but still have a completely segregated separate environment. That was the reason why we went for Cisco ACI.